Broadband data solutions for mobile phones and portable computers have become increasingly popular and necessary. However, providing data solutions that achieve the desired bandwidth may be difficult in certain situations. One example of such a situation is air travel, as conventional mobile phones are very undependable during flight as they do not transmit at a high enough power to maintain communication with the ground networks. Furthermore, many world-wide spectrum regulators have not approved the uncontrolled RF emissions from cellular devices onboard aircraft.
Certain aircraft communication systems have been developed to provide in-flight data solutions. Such a system may utilize a set of custom towers on the ground that point their signals upwards (towards the sky) to communicate with receivers installed on aircrafts. The receivers and the set of custom towers work similarly to that of conventional mobile phones and cell towers. While in-flight data solutions may be provided utilizing such systems, they are very expensive to develop/operate, and they duplicate the mobile phone equipment people already have and would prefer to use. Furthermore, the receivers used in such a system are generally omnidirectional, which may have limited antenna gain due to lack of directionality. Limited antenna gain results in limited data rate, which is undesirable for a broadband data solution. In addition, developing and operating a set of custom towers for communication purposes is subject to various regulations. As a result, for example, certain aircraft communication systems currently in operation are restricted to horizontal polarization only, and there may be very little benefit even if dual polarization antennas are used in such systems.
Conventional ground-based cellular networks may provide a low-cost broadband option for in-flight data solutions. In addition, communication standards such as Long Term Evolution (LTE), 3GPP, UMTS, WiMax and other 4 G and 5 G type technologies as employed without modification by the cellular network carriers may enable more in transit bandwidth capacity compared to the bandwidth provided by the custom towers of the aircraft communication system described above. Therefore, it may be appreciated to provide the ability for an aircraft to communicate with existing ground-based cellular networks and to provide in-flight data solutions utilizing the ground-based cellular networks. In addition, such cellular networks already have established data communication infrastructures, which may be utilized without the need to build custom towers as required in other in-flight data solutions.
However, the elevated position of the aircraft may pose issues with ground networks because of the possibility of illuminating many ground stations/towers in the same band. This may cause the antenna located in the aircraft to induce or transmit signals to and/or receive signals from more than one tower at once. Studies have shown that such behaviors may desensitize receivers at both ends and introduce interferences (for example, as shown in: LTE for UMTS, Harri Holma et al., page 315). Furthermore, the signals provided by the conventional ground stations (cell towers) may not be directed upwardly towards the flying aircraft. Therein lies the need to provide an air-to-ground antenna suitable for communicating with ground stations.